1. Field of the Invention
An aspect of the present invention relates to a cathode electrode structure for a fuel cell, and more particularly, to a cathode electrode structure in which water produced at the cathode electrode does not block an oxygen supplying channel.
2. Description of the Related Art
A fuel cell is an electrical generation system that transforms chemical energy directly into electrical energy through a chemical reaction between oxygen and hydrogen contained in a hydrocarbon group material, such as methanol, ethanol, or natural gas. Fuel cells can be largely divided into direct liquid feed fuel cells in which liquid methanol is directly fed to the fuel cell and proton exchange membrane fuel cells in which hydrogen gas is supplied to the fuel cell.
As depicted in FIG. 1, a unit cell of a direct feed fuel cell has a membrane electrode assembly (MEA) structure having an electrolyte membrane 1 interposed between an anode electrode 2 and a cathode electrode 3. The anode electrode 2 and the cathode electrode 3 respectively include a diffusion layer 22 and 32 for supplying and diffusing a fuel, catalyst layers 21 and 31 where fuel oxidation and reduction reactions occur, and an electrode supporting layer 23 and 33. Conductive plates 4 and 5 are respectively installed on the electrode supporting layer 23 and 33, and the conductive plates 4 and 5 respectively include flow channels 41 and 51.
An electrode reaction of a direct methanol fuel cell (DMFC), which is a type of direct liquid feed fuel cell, includes an anode reaction wherein fuel is oxidized and a cathode reaction wherein hydrogen and oxygen are reduced as described below.CH3OH+H2O→CO2+6H++6e− (Anode reaction)  [Reaction 1] 3/2O2+6H++6e−→3H2O (Cathode reaction)  [Reaction 2]CH3OH+ 3/2O2→2H2O+CO2 (Overall reaction)  [Reaction 3]
Carbon dioxide, hydrogen ions, and electrons are produced at the anode electrode 2 where the fuel is oxidized (reaction 1). The hydrogen ions migrate to the cathode electrode 3 through electrolyte membrane 1. At the cathode electrode 3, water is produced by the reduction reaction (reaction 2) between hydrogen ions, electrons transferred from an external circuit, and oxygen. Accordingly, water and carbon dioxide are produced as the result of the overall electrochemical reaction (reaction 3) between methanol and oxygen.
The flow channel 41 is formed on a surface of the conductive plate 4 facing the cathode electrode 3. Water produced at the catalyst layer 31 of the cathode electrode 3 may block the flow of air supplying through the flow channel 41, and thus the stable power generation of the fuel cell may be obstructed.